1. Field of the Invention
This invention relates to the formation of integrated circuit structures. More particularly, this invention relates to inhibition of peeling and resultant particle and/or flake formation at the edge of a semiconductor substrate during formation of a integrated circuit structure thereon.
2. Description of the Related Art
In the formation of integrated circuit structures, multiple layers of electronic structure are formed, including at least one layer of active devices and a plurality of metal interconnect layers. Most, if not all, of the layers involve some sort of patterning using photolithography wherein a layer of photoresist is blanket deposit over the surface of the semiconductor substrate, then exposed to a pattern of light through a reticle, and the exposed portions of the photoresist are removed by a developer solution (when positive resist is used), leaving, in the photoresist layer, an exact replica of the pattern in the reticle.
While such photolithography is in widespread use, it was recognized many years ago that the blanket deposition of photoresist on the upper surface of the substrate, e.g., by spin-on of the photoresist film, resulted in the undesirable formation of particles or flakes when the end edge of the substrate was grasped either manually or by mechanical means during further steps such as metal deposition processes/thermal cycles, either to move the substrate or to secure it during processing.
This problem of particle/flake formation was addressed in Allen U.S. Pat. No. 4,518,678 which proposed to form a photoresist-free lip on the upper surface of the substrate adjacent the end edge of the substrate by directing a stream of a solvent for the photoresist against the end edge of the substrate.
It was also recognized in the prior art that in the practice of photolithography, one could not tolerate exposure of the photoresist to a reflected beam of the pattern of light from the reticle since the reflected light usually was reflected back into the photoresist at an oblique angle rather than at 180xc2x0, thus destroying the sharpness of the light image formed in the photoresist.
This resulted in the practice of providing an antireflective surface directly beneath the photoresist layer to prevent reflection back through the photoresist of the pattern of light originally projected onto the photoresist layer from the reticle.
Since such an antireflective surface was almost always desirable whenever a resist layer was used, opaque coatings became commercially available which, although not photosensitive, were removable by liquid solvents just as the light exposed portions of the photoresist (although the same solvent is not used for both).
Also since the antireflective coating layer (ARC layer), or bottom antireflective coating layer (BARC layer) is the layer beneath the photoresist layer, and it was considered desirable to have the ARC or BARC layer beneath all of the photoresist layer, it became the practice to spin on the ARC/BARC layer to the end edge of the semiconductor substrate and then to remove the portion of the ARC layer adjacent the end edge of the substrate by directing a flow of solvent against the end edge of the ARC layer, i.e., to remove the portion of the ARC layer adjacent the end edge of the substrate by chemical means just as had been previously done with the photoresist layer.
It then became the custom to spin on the photoresist layer over the ARC layer and to expose the outer edge of the photoresist layer to radiation followed by development of the photoresist, resulting in the prior art structure shown in FIG. 1 wherein an ARC layer 10 is formed over a semiconductor substrate or wafer 2, with the edge 14 of ARC layer 10 terminating adjacent end edge 4 of substrate 2; and a photoresist layer 20 formed over ARC layer 10, with an outer edge 24 of photoresist layer 20 terminating a greater distance from end edge 4 of substrate 2.
However, as the sizes of integrated circuit structures continued to shrink and tolerances became smaller and smaller, it became apparent that the unevenness of edge 14 of ARC layer 10, as shown magnified at 16 in FIG. 2, resulting from the solvent spray directed toward the end edge of the substrate, was not satisfactory since particle/flake formation still occurred when wide portions of the resulting uneven edge 16 of ARC layer 10 came into contact with substrate-engaging structures.
In accord with the invention, a photoresist-free and ARC-free lip on the periphery of the upper surface of a semiconductor substrate adjacent the end edge of the substrate is formed by the steps of:
a) forming an ARC layer on one surface of a semiconductor substrate;
b) chemically treating the ARC layer to chemically terminate the ARC layer a first distance from the end edge of the substrate;
c) forming a photoresist layer over the semiconductor substrate and over the ARC layer thereon; and
d) exposing the peripheral portion of the photoresist layer to radiation followed by development of the exposed peripheral portion of the photoresist layer to photolithographically terminate the photoresist layer a second distance from the end edge of the substrate wherein the second distance is smaller than the first distance.